Process for producing viscose regenerated cellulose fibers



- Oct- 29, 1953 'rosHlRo owAsHl ETAL 3,108,849

PROCESS FOR PRODUCING VISCOSE REGENERATED cELLULosE FIBERS Filed oct. 25, 1961 5 Sheets-Sheet l Fig- Z/7504 (a/o) IN VEN TOR.

PROCESS FOR PRODUCING VISCOSE REGENERATED CELLULOSE FIBERS Filed Oct. 25, 1961 3 Sheets-Sheet 3 00L 29, 1963 TosHlRo owAsHl Erm. 3,108,849

Aged a/ka/i ce//u/ose Carbon disulfide Wafer [or aqueous cous/c soda) Disso/vin Viscose Sulfur/'c acid @aqu/amg sodium su/fae bGf/I zinc su/foie wafer Spion/77g Produc TOH//Q 0 Dawes/W, [Z39/ INVENTOR.

United States Patent O 3de-$15849 PRGCESS FR PRDUCENG VSCOSE REGEN- ERATED CELLULSE FEBERS Toshiro washi, Shinsakuramachi, Toyama-shi, Keigo noe, Nukuicho, Nerima-ku, Tokyo, and Hiroshi to and Atsushi Kawai, Kurokawa, Ggatacho, @take-shi, apan, assignors to Mitsubishi Rayon Co., Ltd., Tokyo, `tapan, a corporation of Eapan Filed Get. 2S, 1961, Ser'. No. 147,507 Claims priority, appiiwtion lapan (let, 27, 1960 5 Claims. (Cl. 18-54) The present invention relates to an improved process for preparing viscose regenerated cellulose liber having properties of a high Youngs -modulus in wet state, a low Water swelling, a high strength, and a high knot strength and a good dyeability and having a tineness of 0.5-30 denier, and to an improved process for preparing such denier.

Up to this time, various improved methods have been provided to manufacture a viscose regenerated cellulose ber. For example, in the U.S. Patents No. 2,535,044 and No. 2,529,750, a method has been described where a viscose solution added with amines or polyethylene oxide derivatives is extruded into a coagulating bath containing 3% or more of zinc sulfate to spin the ber while the solution is in an unripened state. However, the ber thus obtained, in spite of having a low water swelling, a high strength, and a high fatigue resistance, posses a low Youngs modulus in Wet state, so that the fabric obtained therefrom is inadequate for a practical usage because of a large shrinkage after washing and a bad dimensional stability. It has also been proposed that a highly viscous viscose solution be subjected to a spinning process in an unripened state as indicated in the U.S. Patent No. 2,732,- 279. The fiber prepared by the said lmethod possesses a low water swelling and a high Youngs modulus in wet state, while it has an extremely lower knot strength and a lower fatigue resistance, so that the fabric prepared therefrom has a poor abrasion resistance.

Furthermore, it has been proposed that fiber having a high Youngs modulus in Wet state may be prepared by extruding a viscose solution into a coagulating bath which contains sulfuric acid, sodium sulfate and Zinc sulfate as described in the Belgian Patents No. 573,565 and No. 581,- 631. However, the bers obtained by these methods have inferior properties such as strength, knot strength, fatigue resistance and dyeability.

Consequently, the object of the present invention is to provide an improved process for manufacturing viscose regenerated cellulose fiber having a high Youngs modulus in -Wet state, a low Water swelling, a high strength, a high knot strength and a good dyeability,

These objects are, in accordance with the present invention, attained by extruding a viscose solution having a viscosity of 100-500, an alkali concentration of 3 to 5 percent and a salt point of from 9 to 20 into a coagulating bath containing 0.02-0.04% of zinc sulfate, l-l0% of sodium sulfate and a limited concentration of sulfuric acid provided by the following equations and being kept at a temperature of between '10 and 30 C.;

The minimum sulfuric acid concentration (percent) :033A+1o.u-2s-5C+0.13\/5.-0.24

The maximum sulfuric acid concentration (percent) :0.38/1+0.02B+2C+0.27\/D-.05

tl/i@ Patented 01st. 29, i953 ICC wherein A represents an alkali concentration (percent) in the viscose solution, B is a sodium sulfate concentration (percent) in a coagulating bath, C is a zinc sulfate concentration (percent) in a coagulatin-g bath, and D stands for a single filament denier of the ber to be spun.

The viscose regenerated cellulose liber prepared by the -method'shown in FIG. 6, a flow sheet of the process, has a higher Youngs modulus in wet state, a lower Water swelling, a higher strength, especially in Wet state, andv a higher knot strength as compared with those of viscose fibers obtained by a conventional method. Consequently, the fabric converted-from the ber prepared by the method of this invention has characteristics of an extremely small shrinkage after Washing, an extremely high dimensional stabiility, a high tear strength, a high abrasion resistance, and a good dyeability, and what is more, when the textile is subjected to a resin treatment, thus treated textile has also a good crease resistance, and a good abr-asion resistance.

Following is a detailed description of the invention.

-In the method of this invention, various kinds of dissolving pulp may be utilized and sufficient-ly good quality fiber may successfully be prepared therefrom.

Referring to the flow sheet, FG. 6, the pulp is steeped into an aqueous caustic soda solution, pressed to remove the excess amount of aqueous caustic soda solution therefrom and shredded. The shredded alkali cellulose is xanthated after ageing; however, the alkali cellulose may be xanthated immediately after shredding.

For the purpose of xanthation of alkali cellulose, it may be preferable to employ 40% to 50%, based upon the weight of cellulose in the alkali cellulose, of carbon disulde. Thus the produced sodium cellulose xanthate is added with Iwater and aqueous caustic soda solution and dissolved therein to make a viscose solution.

The degree of polymerization of cellulose in the viscose solution, is preferred to be in the range from 350 to 700, and especially `from 400 to 500.

The viscosity of the viscose solution is an important factor of the present invention, and it must be a value Within a range from to 500 poises at spinning.

When the viscosity of viscose solution is less than 100 poises, the solution can not effectively be spun, and when more than 500 poises, it may also be difficult to spin and thus the obtained ber has a deteriorated quality. The most preferable viscosity is -400 poises.

The cellulose concentration of viscose may advantageously be determined in accordance with the degree of polymerization of the cellulose. For example, when the degree of polymerization of cellulose is 430, it is preferable to employ about 7% of the cellulose concentration. The alkali concentration in the viscose solution is settled within a range from 3% to 5%. When the alkali concentration is out of these limits, it results in a decrease in spinnability of the solution.

The obtained viscose is subsequently iiiltered, deae-rated, ripened and extruded into a coagulating bath.

The degree of ripening of the viscose at the time of spinning is also one of the important factors of the present invention. The salt point of the viscose solution at spinning time is Within the limits of between 9 and 20. The liber prepared from the viscose having a salt point less than 9 has a lower strength and a higher water swelling. In addition an excessively high salt point of more than 20 results in the spinning conditions becoming worse. The most preferable salt point is between 12-16.

As to a coagulating bath of the present invention, a bath containing zinc sulfate, sodium sulfate and sulfuric acid may be employed. The zinc sulfate concentration of the coagulating bath is one of the most important factors of the present invention, and it must be within the limits of from 0.02% to 0.04%. When the zinc sulfate concentration is less than 0.02%, the fiber thus obtained will have inferior characteristics such as knot strength and dye absorption, while in case of more than 0.04%, it will deteriorate the properties such as strength in wet state, knot strength and dye absorption.

The curve 1 shown in FIG. 1-FIG. 3 represents the correlation between the zinc sulfate concentration in a coagulating bath and the quality of fiber obtained by the method which comprises extruding a viscose solution containing 7% of cellulose and 4% of alkali and having a viscosity of 170 poises and salt point of 16, into a coagulating bath containing 1.5% of sodium sulfate, 1.33% of sulfuric acid and various concentrations of zinc sulfate, the temperature of which is kept at C. and the immersion length of which is 40 cm., through a spinneret (0.06 hole diameter and 1000 holes), subjecting the freshly spun thread to 80% stretch within air, taking the thread on a reel at a spinning velocity of 18 m./ min. and then subjecting to refining in accordance with a conventional method. From the said curves, a specific effect of zinc sulfate employed in the present invention can clearly be understood.

The concentration of sodium sulfate may practically be within the limits of between 1% and 10%, and preferably be from 1% to 5%. When the concentration of sodium sulfate becomes more than 10%, it is difficult to spin the viscose solution. An employment-of less than 1% is not practicable from an economical point of view.

The concentration of sulfuric acid has a close correla tion with the lalkali concentration of viscose solution, sodium sulfate concentration and zinc sulfate concentration of coagulating bath, and with single filament denier of the ber to be spun. lt must. be within the limits provided by the following equations:

The minimum sulfuric acid concentration (percent) wherein A represents the concentration (percent) of alkali in a viscose solution, B is the concentration (percent) of sodium sulfate in a coagulating bath, C is the concentration (percent) of zinc sulfate in a coagulating bath, and D stands for the single lilament denier (d.) of the ber to be spun. When the concentration of sulfuric acid is below the above defined limits, it is vdiiiicult to spin the viscose solution, and on the other hand, when the concentration is above these limits, it is observed that the spinnability of the solution delinitely decreases. The specific effect of zinc sulfate is not known, but the obtained liber has a lower knot strength and a lower dye absorption.

The curve 2 shown in FIG. l-FIG. 3 represents the correlation of between the zinc sulfate concentration and the quality of fiber prepared by using the same conditions with those of curve l except that the concentration of sulfuric acid is 2.3%.

rFrom comparison between curve 1 and curve 2 in FIG. l-FIG. 3, one may easily determine that when the sulfuric acid concentration of the coagulfating bath becomes 2.3%, the effect of zinc sulfate can not be ascertained as in the case with 1.33% of sulfuric acid concentration.

The minimum sulfuric acid concentration in a coagulating bath of the present invention, as clearly shown from the above mentioned equation, it becomes higher and higher in accordance with the increases in the concentration of alkali in the viscose solution, in the concentration of sodium sulfate in a coagulating bath and in the single filament denier of the fiber to be spun, while it becomes lower and lower in accordance with the increase in the zinc sulfate concentration.

As to the maximum sulfuric acid concentration, it becomes higher and higher in accordance with the increases in the alkali concentration in the viscose solution, in the sodium sulfate concentration and the zinc sulfate concentration in a coagulating bath, and also in the single filament denier of the fiber to be spun.

The sulfuric acid concentration limits of the present invention, however, have been derived from the results of many experiments.

Speaking o-f the temperature of coagulating bath, a temperature of between 10 and 30 C. may practicably be employed, and its preferable range is from 15 to 25 C. When a temperature of more than 30 C. is employed, it must result a diiiicult problem of spinning.

If an excess resistance is `given to the freshly spun thread in a coagulating bath, the obtained liber is inferior in its quality. Consequently, in order to decrease the resistance and to increase the spinning velocity, a stabilizing tube is provided near the spinncret to make the coagulating bath liquid flow in the same direction as the liber therethrough. This method is especially effective in the case when a spinneret having less than holes is employed.

A preferable immersion length of the coagulating bath is 20-50 cm. When the immersion length is out of this range, it results in decreased spinnability. The thread brought out from the coagulating bath is stretched in the air or in a second bath. The fiber stretched inthe second bath has a higher tensile strength and higher knot strength than that stretched in the air. However, it is preferable to stretch the liber in -a second bath. Speaking of the second bath, it may be preferred to employ a hot water bath containing or not containing less than 4% of sulfuric acid, and being kept at more than 50 C.

Thus stretched liber is then subjected to a refining process according to a conventional method. However, in the present invention, it is desirable `to employ the regeneration process prior to the refining.

The following are examples of the present invention.

Example 1 A wood pulp, the polymerization degree of which was 800, was steeped into 19% :aqueous caustic soda solution containing 0.85% of hemicellulose at 22 C. for 50 minutes, and then pressed to 2.75 times the dried pulp. Thus obtained alkali cellulose was shredded at 25 C. for 1 hour, and aged for 15 hours at 24 C. to give an alkali cellulose having 500 of polymerization degree. To this 47%, based upon the weight of cellulose in the alkali cellulose, of carbon disulfide was added. The alkali cellulose was then subjected to Xanthation at 26 C. for 140 minutes and thus obtained sodium cellulose xanthate was diluted with aqueous caustic soda solution and water to give a viscose solution containing 7% of cellulose and 4% of alkali. The polymerization degree of cellulose in the viscose solution was 430. This viscose solution was liltered, deaerated, ripened. The resulted viscose having 168 poises of viscosity and a salt point of 16 was extruded through a spinneret (0.06 mm. hole diameter and 1000 holes) into a ooagulating bath containing 0.03% of zinc sulfate, 1.5 of sodium sulfate and 1.4% of sulfuric acid, the 'temperature of which was kept at 20 C., at a salt point of 16. The extruding rate of the viscose was 53 cc./min. The thread brought out from the coagulating bath was subjected to 100% stretch within the second bath containing 1% of sulfuric acid at 50 C., and then to a refining process according to a conventional method. The spinning velocity was 28 m./min. Following is the comparison of the quality of thus obtained fiber with that of conventional viscose rayon staple for textile use.

Tensile Elongation Knot Water Dye Wet Strength (g./d.) (percent) strength retenabsorpmodulus Denier (g./d.), tion tion at (d.) condi- (pcr- (perelongation Condi- Wet Condi- Wet tioned cent) cent) (gld.) tioned tioned Example ofthe invention." 1. 5 3. 85 3. 13 11.0 14. 7 2.14 69 G4 1. 3S Conventional rayon Staple-- 1. 5 2. 89 1.82 18. 5 22. 0 1. 68 109 58 0. 18

N ern-Wet modulus oi ber means force (gld.) required to elongate the fiber by 5% in Wet state.

Referentz'al Example 1.-For the purpose of reference, the same procedures as in the Example 1 were repeated except that ythe following baths were employed respectively instead of the previously described coagulating bath.

(A) A coagulating bath containing 1.5% of sodium sulfate yand 1.6% of sulfuric acid, which did not contain zinc sulfate, and kept at 20 C.;

(B) A coagulating bath containing 0.1% of zinc sulfate, 1.5% of sodium sulfate, and 1.4% of sulfuric acid and being kept at 20 C.;

(C) A coagulating bath containing 0.03% of zinc sulfate, 1.5% of sodium sulfate and 2.8% of sulfuric acid and being kept at 20 C.

Referentin] Example `2.-he same procedure as in the Example 2 was repeated except that a coagulating bath containing 1.8% of sodium sulfate and 1.7% of sulfuric acid (zinc sulfate was not included therein), and being The qualities of thus obtained bers were shown as kpt at 20 C. Was employed. The quality of thus obfollowing:

Tensile Elongation Knot Wet strength (g./d.) (percent) strength Water Dye abmodulus Denier (d.) (g./d.), retention sorpt1on at 5% condi- (percent) (percent) elongation Condi- Wet Condi- Wet tioned (t/(L) tioned tioned 3. 54 2. 88 7. 8 9. G 0. 84 69 52 1. 12 3. 02 2.12 13. 9 20. 2 1. 58 78 51 O. 58 3. 18 2. 21 8. l 10. 8 1. 11 72 2S O. 66

Example 2 tained fiber Was shown as following.

A Wood pulp, the polymerization degree of which Was about 800, was steeped als a slurry into 17.5% aqueous caustic soda solution containing 1.6% of hernicellulose, kept at 45 C., pressed to 2.8 times the dried pulp, shredded, and theredter aged for 1.5 hours within a room kept at 27 C.

To this 45%, based upon the Weight of cellulose in an alkali cellulose, of carbon disuliide was added, the mixture was subjected to a xanthation at 26 C. for 140 minutes. Thus produced sodium cellulose xanthate was diluted with caustic soda and water to give a viscose solution containing 7% of cellulose and 4% of alkali. The polymerization degree of cellulose in the viscose was 430. The viscose solution Was ltered, deas-rated, and ripened. The resulted viscose having 162 poises of viscosity and salt point of 14 was extruded. Through `a spinnereit (0.07 mm. hole diameter and 6000 holes) into a coagulating bath, the irnmersion length of which was cm. and the temperature of which was kept at 20 C., containing 0.03% of zinc sulfate, 1.8% of sodium sulfate and 1.43% of sulfuric acid, at a salt point of 14. rThe thread brought out from the coagulating bath Was subjected to 70% stretch, to a regeneration process Within a bath which contained 2% of sulfuric acid and was kept at 80 C., and then subjected Ito rehning in accordance with a conventional method. The quality of thus obtained liber was shown as following:

Tensile Elongation strength (percent) Knot Water Dye (gld.) strength retenabsorp- Donier (g./d.), tion tion condi- (per- (per- Condi- Wet Cond- Wet tioned cent) cent) tioned toned Example 3 A Wood pulp, the polymerization degree of which was 800, was dipped into 19% aqueous caustic soda solution at 20 C. for 50 minutes, pressed to 2.75 times the dried pulp, shredded at 26 C. for 1 hour and then aged at 26 C. for 18 hours.

To the obtained alkali cellulose, 40%, based upon the Weight ot cellulose in an alkali cellulose, of carbon disulfide was added. The mixture Was then subjected to xanthation at 27 C. for 150 minutes. The produced sodium cellulose xanthate was diluted with caustic soda and water to give a viscose solution containing 7.5% of cellulose and 5% of alkali.

The polymerization degree of cellulose in the viscose solution was 400.

The viscose solution was iltered, deaerated, and then ripened at 3 C. for a short while. The viscose solution having poises of viscosity and a salt point of 16 Tensile Elongation Wet A strength (percent) Knot Water Dye modu- Denier (gld.) strength retenabsorplus at (g./d.), tion tion (d.) condi- (per- (perelon- Cpndi- Wet Condi- Wet tioned cent) cent) gation tioned tioned (gld.)

Example 4 A Wood pulp, the polymerization of which w 800, was steeped into 19% aqueous caustic soda solution at 22 C. for 50 minutes, pressed to 2.75 times the dried pulp, shredded at 26 C. for 1 hour, and aged at 26 C. for 8 hours to give an alkali cellulose. To the alkali cellulose, 47%, based upon the Weight of cellulose in the said alkali cellulose, of carbon disulfide was added. The alkali cellulose was subjected to Xanthation at 26 C. for 140 minutes. The obtained sodium cellulose Xanthate was diluted with aqueous caustic soda solution and water to give a viscose solution having 7.3% of cellulose and 4.5% `of alkali. The polymerization degree of cellulose in the viscose Was 500. The viscose solution was ltered, deaerated and then ripened. The obtained viscose solution having 400 poises of viscosity and a salt point of 16 was extruded through a spinneret (0.07 mm. hole diameter and 1000 holes) into a coagulating bath containing 0.02% of zinc sulfate, 1.0% of sodium sulfate and 1.35% of sulfuric acid and being kept at 18 C. The immersion length of the coagulating bath was 30 cm. The thread brought out from the coagulating bath was subjected to 105% stretch in the second bath containing 4% of sulfuric acid and being kept at 50 C., and then to a rening process. The quality of thus obtained fiber was shown as follows:

A Wood pulp, the polymerization degree of which was 800, was steeped into 19% aqueous caustic soda solution at 20 C. for 50 minutes, pressed to 2.75 times the dried pulp, shredded at 26 C. for 1 hour, and then aged at 26 C. for 8 hours. To the obtained alkali cellulose, 50%, based upon the weight of cellulose in the alkali cellulose, of carbon disulfide was added. The alkali cellulose was subjected to a Xanthation at 26 C. for 150 minutes to give sodium cellulose Xanthate. The sodium cellulose Xanthate was diluted with aqueous caustic soda solution and water to give a viscose solution containing 6% of cellulose and 3.0% of alkali. The polymerization degree of cellulose in the viscose was 500. It was filtered, deaerated and r-ipened. Thus obtained viscose solution having 200 poises of viscosity and a salt point of 16 was extruded through a spinneret (0.08 mm. hole diameter and 1000 holes) into a coagulating oath containing 0.03% of zine sulfate, 1.5% of sodium sulfate and Tensile strength (sid.)

Wet modulus at Elongation (percent) Water retention (Dercent) D ye absorp- (tion percent) Denier elongation (sld.)

Conditioned Wet Conditioned Wet Example 6 A wood pulp, the polymerization degree of which was 1000, was steeped into 19% aqueous caustic soda solution at 20 C. for 50 minutes, pressed to 2.75 times the dried pulp, shredded at 20 C. for 1 hour, and then ripened at 20 C. for 7 hours. To the alkali cellulose, 47%, based upon the weight of cellulose in the alkali cellulose, of carbon disulfide was added. The alkali cellulose was subjected to Xanthation at 26 C. for 150 minutes to give :sodium cellulose Xanthate. The sodium cellulose Xanthate was diluted with aqueous caustic soda solution and water to give a viscose solution containing 4.5% of cellulose and 4.5% of alkali. The polymerization degree oi cellulose yin the viscose was 600. The Viscose solution Was filtered, deaerated an dripened. `Thus obtained viscose solution having poises of viscosity and a salt point of l5 was extruded through a spinneret (0.04 mm. hole diameter and 1000 holes) into a coagulating bath contain ing 0.02% of Zinc sulfate, 1.5% of sodium sulfate and 1.4% of sulfuric acid and being kept at 18 C. The immersion length of the coagulating bath was 20 cm. The thread brought out from the coagulating bath Was subjected to 98% stretch in the second bath containing 2% of sulfuric acid at 80 C. and then subjected to refining. The quality of thus obtained liber was shown as follows:

Tensile strength (ski.)

Elongation (percent) Wet modulus at elongation (iL/d Water retention (DGP cent) Dye Denier absorption (per- Condicent) tioned Condi- Wet tioned Wet Example 7 A Wood pulp, the polymerization degree of which was 800, was steeped into 19% aqueous caustic soda solution at 20 C. for 50 minutes, pressed to 2.75 times the dried pulp, shredded at 26 C. for 1 hour, land then aged at 26 C. for 18 hours.

Thus obtained alkali cellulose was added with 43%, based iupon the Weight of cellulose in the alkali cellulose, of carbon disuliide. The alkali cellulose solution was xanthated at 27 C. for 150 minutes to give sodium cellulose xanthate. The sodium cellulose Xanthate was diluted by adding aqueous caustic soda solution and Water to give a ,viscose solution containing 9% of cellulose and 5% of alkali. The polymerization degree of celluose in the viscose was 400. The viscose solution was iiltened, deaerated and ripened. Thus obtained viscose solution, which had 500 poises of viscosity and a salt point of 12, Was extruded through a spinneret (0.2 mm. hole diameter and 500 holes) into a coagulating bath containing 0.04% of zinc sulfate, 2.0% of sodium sulfate and 3.3% of sulfuric acid and being kept at 25 C. The

immersion length of the coagulating bath was 50 cm. The thread brought `out of the coagulating bath was subjected to 35% stretch in the second bath containing 3% of sulfuric acid and being kept at 70 C., and then subjected to reiining. The quality of thus obtained fiber w-as shown as following:

This fiber had a circular cross section.

Example 8 A wood pulp, the polymerization of which was 800, was steeped as -a slurry into 17.5% aqueous caustic sod-a solution at 45 C., ypressed to 2.8 times the dried pulp, shredded and aged in a room kept at 27 C. for 4 hours.

To the obtained alkali cellulose, 60%, based upon the weight of cellulose in the alkali cellulose, of carbon disulde was added, and the alkali cellulose solution was subjected to xanthation at 26 C. for 140 minutes to give a sodium cellulose xanthate. The sodium cellulose xanthate was diluted with aqueous caustic soda solution and Water to give a viscose solution containing 7% of celluose and 4% of alkali. The polymerization degree of cellulose in the viscose was 380.

The viscose solution was then iltered, deaerated and ripened. The obtained viscose having 100 poises of viscosity and a salt point of 20 was extruded through a spirineret (0.07 mm. hole diameter and 50 holes) into a coagulating bath containing 0.03% of zinc sulfate, 2% of sodium sulfate and 1.3% of sulfuric -acid and being kept at 20 C.

In this case, a glass stabilizing tube of 8 mm. inner diameter and 40 cm. length was settled at the position 1 cm.off from the spinneret. :T he coagulating bath liquid was made llow with the thread and in the same direction as the thread Within the glass tube. The flow velocity of the coagulation solution in the glass tube was 18 m./min., and the peripheral speed ofthe iirst roller was 20 rn./ min. The gel liber passed through the glass tube was subjected to 170% stretch within air.

The quality of thus 'obtained fiber was shown as following:

Tensile Elongation Wet strength (percent) Knot Water Dye modu- Dcnier (g./d.) strength retenabsorplus at (g./d.), tion tion 5% (d.) condi` (per- (perelon- Ccndi- Wet Condi- Wet tioned cent) cent) gation tioned toned (gld.)

Example 9 aqueous caustic soda and water to give a viscose solutioncontaining 7% of cellulose yand 4% of alkali. The polymerization degree of cellulose in the viscose solution was 430. The viscose solution was then iiltered, deaerated and aged. The ripened viscose solution having 208 poises of viscosity and a salt point of 18 was extruded through a spinneret (0.06 mm. hole diameter and 1000 holes) into a coagulating bath containing 0.04% of zinc sulfate, 10% of sodium sulfate and 1.7% of sulfuric acid and being kept at 20 C.' The irrnnersion length of the coagulating bath was 40 cm. The thread brought :out from the coagulating bath was subjected to 110% stretch in the second bath containing 2% of sulfuric acid and being kept at 80 C., and then subjected to a refining process.

The quality of thus obtained `fiber was shown as follows:

Tensile Elongation Wet strength (percent) Knot Water Dye modu- Denier (g./d.) strength retenabsorplus at (g./d.), tion tion 5% (d.) condi- (per- (perelon- Condi Wet Condi- Wet toned cent) cent) gatlon tioned tioned (g-/d-) Example 10 Tensile Elongation Wet strength (percent) Knot Water Dye modu- Demer (gld.) strength retenabsorplus at (g./d.), tion tion 5% (d.) v eondi- (per- (perelon- Condi- Wet Condi- Wet tioned cent) cent) gation tioned tioned (g./d.)

Example 11 The same vislcose solution as shown in Example 1 was extruded through a spinneret (0.09 min. hole diameter and 1500 holes) into a coagulating bath containing 0.03% of zinc sulfate, 1.5% of sodium sulfate and 1.9% of sulfuric acid and being kept at 20 C. The thread brought out from the coagulating bath was subjected to 70% stretch Within air and then to a rening process. The obtained liber had the following properties:

Tensile Elongation Wet strength (percent) Knot Water Dye modu- Denier (g./d.) strength retenabsorplus at (g./d.), tion tion 5% (d.) eondi- (per- (perelon- Condi- Wet Condi- Wet tioned cent) cent) gation tioned tioned (g./d.)

Example 12 The same viscose solution as shown in Example l Was extruded through a Spinnerei (0.10 mm. hole diameter and 1000 holes) into a coagulating bath containing 0.03% of zinc sulfate, 1.5% of sodium sulfate and 2.6% of sulfuric acid and being kept at 20 C. The thread brought out from the coagulating bath was subjected to 65% stretch within air, and then subjected to reiining.

ecosse-a The ber had a circular cross section.

Example 13 The same viscose solution as shown in Example 2- was extruded through a spinneret (0.08 mm. hole diameter and 6000 holes) into a coagulating bath containing 0.03% of zinc sulfate, 1.6% of sodium sulfate and 1.65% of sulfuric acid and being kept at C. The immersion length of the bath was 45 cm. The extruding rate of the viscose was 320 cc./min. The thread removed from the coagulating bath was subjected to 45% stretch within air, to a regeneration process in the second bath containing 2% of sulfuric acid and being kept at 80 C., and then subject to refining. The spinning velocity was 14 m./ min. Thus obtained fiber had the following properties.

Example 14 The same viscose solution as shown in Example 2 was extruded .through a spinneret (0.12 mm. hole diameter and 700 holes) into a coagulating bath, the immersion length of which Was 45 cm. and the temperature of which was kept'at 20 C., containing 0.03% of zinc sulfate, 3.2% of sodium sulfate and 2.1% of sulfuric acid. The extruding rate of the viscose solution was 300 cc./min. The thread removed from the coagulating bath was subjected to 35% stretch in the air, and treated in a regeneration process in the second bath containing 2% of sulfuric acid maintained at 80 C., and then subjected to refining. The spinning velocity was 22 m./min. Thus obtained fiber had the following properties.

The ber obtained in the present example had a circular cross section.

What We claim is:

1. In a process for producing viscose regenerated cellulose iibers having a denier of 0.5 to 30, a method comprising extruding a viscose solution containing from 3 to 5% of alkali and having a viscosity of from 100 to 500KV poises and a salt point or" from' 9 `to 20, into a coagulating bath being kept at a temperature of from 10 to 30 C. and containing from 0.02 to 0.04% of zinc sulfate, from 1 to 10% of sodium sulfate, and sulfuric acid at a concentration within the range dened by the equations:

minimum sulfuric acid concentration` (percent) :0.33.4+a.0\2B5c+o.13\/50.24 and maximum sulfuric acid concentration (percent) wherein A represents the alkali concentration (percent) fate concentration (percent) in the coagulating bath and D stands for the single iilament denier (d.) of a ber to be spun.

2. A method according to claim 1, wherein said viscose solution has a cellulose polymerization degree of from 400 to 500, a viscosity of from to 400 poises and a salt point of from 12 to 16 is extruded into a coagulating bath containing from 1 to 5% of sodium sulfate and having an immersion length of from 20 to 50' cm.

3. A method according to claim 1 which comprises xanthating an alkali cellulose with the addition of carbon disulfide in an amount 40 to 50% by weight on the basis of the cellulose in said alkali cellulose, dissolving the xanthated alkali cellulose in an aqueous caustic solution to form a Viscose solution containing from 3 to 5% of alkali having a cellulose polymerization degree of from 400 to 500, a viscosity of from 150 to 400 poises, and a salt point of from 12 to 16, extruding the solution into a coagulating bath containing from 0.02 to 0.04% of zinc sulfate, from 1 to 5% of sodium sulfate and sulfuric acid at a concentration Within the range defined by the equa` tions minimum sulfuric acid concentration (percent)l wherein A represents the alkali concentration (percent) in the viscose solution, B is the sodium sulfate concentration (percent) in the coagulating bath, C is the zinc sulfate concentration (percent) in the coagulating bath, and D stands for the single filament denier (d.) of a fiber to be spun, and then' stretching the resulting filaments inV the second bath containing less than 4% of sulfuric acid and being kept at a temperature of more than 50 C.

`4. A method accord-ing to claim l, wherein a thread brought out from the coagulating bath is then subjected References Cited in the kle of this patent UNITED STATES PATENTS 2,997,365 smith etai Aug. 22, 1961 

1. IN A PROCESS FOR PRODUCING VISCOSE REGENERATED CELLULOSE FIBERS HAVING A DENIER OF 0.5 TO 30, A METHOD COMPRISING EXTRUDING A VISCOSE SOLUTION CONTAINING FROM 3 TO 5% OF ALKALI AND HAVING A VISCOSITY OF FROM 100 TO 500 POISES AND A SALT POINT OF FROM 9 TO 20, INTO A COAGULATING BATH BEING KEPT AT A TEMPERATURE OF FROM 10* TO 30* C. AND CONTAINING FROM 0.02 TO 0.04% OF ZINC SULFATE, FROM 1 TO 10% OF SODIUM SULFATE, AND SULFURIC ACID AT A CONCENTRATION WITHIN THE RANGE DEFINED BY THE EQUATIONS: 